To re-cap or not re-cap .....

[Krisbee]

My old RA-820BX3, owned by me since new, is pretty long in the tooth now. It's been idle for a while but I've be wondering if it's worth getting this thing re-capped. It's got a pair of pretty large power caps etc.

It's never been serviced, I would have thought the quiescent currents and dc offsets should be checked. I haven't taken the lid off for a while and can see through the top vents that at least one resistor has the paint flaking off, which could mean it's outside it's power spec.

There are no faults as such, so do I adhere to "if ain't broke don't fix it" or do I invest a little money to perk it up and get some more use out of it? :scratch:

Of course, I'd have to find someone to do it, and sods law says that after spending money it will bust. You know, I really must start to look on the bright side of life.

[DSJR]

One problem you and I have (old but good CRT tellies in my case) is that old and now cheap gear like the Rotel will cost more than their value to get a third party to work on them in labour charges...

Our son's 24" JVC widescreen TV (WTV24 or somesuch) has had a slowly contracting frame with slight picture darkening for a month or so and today it tripped out after ten or so seconds of use. It's going to be £55 at least and only cost me £50 last year.........)

The saying about "fixing" non broken gear does hold true and I suspect that the better caps fitted to your Rotel would have been well specified in the first place as this was one area the BX series was superior (power supplies up to the job).

Seriously, I'd leave well alone unless you wish to bodge and don't mind if it gets blown up by accident......

Perhaps you could learn to solder well and then try doing it up yourself :)

[Ali Tait]

Yep,I'd second that.Do it yourself if you can,you'll save a fortune.

[Krisbee]

Advice heeded. Rotel have a fixed charge of around £100, which is too expensive. £50 labour is about the cheapist I could find for anyone to re-cap. DIY is not really an option for me. I've no skills, experience or kit.

No one has picked up on the "checking quiescent currents and dc offsets" bit. How important is this in a sand amp? I did find a "technical manual" on line which shows the test points and procedure to follow. But apart from being yellow, I don't even have a decent multimeter, and I have no idea what might happen trying to tweak a small VR after 20+ years.

[DSJR]

SAND AMP? Valves use glass and where does that come from????

Seriously, if the offsets had gone way off, you'd have noticed by now in terms of hotter than usual running or audible distortion on one channel. Old Naims drifted because of the old fashioned way the circuit is designed coupled with the manufacturers implementation and the fact that many users left them on 24/7, which isn't always a good thing if the components are rated at their voltage limits (I'd suggest that supply rails using 37V should perhaps have 63V caps instead of 40V ones - my Crowns use 40V working caps on a 30V rail and these were designed to be left on in studios all the time).

[Krisbee]

I meant solid state. God knows why I should start talking gibberish. Must have read it elsewhere and it stuck in my head. It's a poor term, and as you were quick to point of course glass contains silica which is silicon oxide and so is not entirely removed from transistor silicon.

There's no audible distortion, but it does seem a bit hot cf my RA-01 and there's certainly paint flaking on at least one resistor.

If I''ve read the schematic correctly, the RA-820bx3 has 41v rails with 50v power caps.

[Ali Tait]

It's not gibberish IMO.Some think it's a derogatory term-I don't mean it that way,it's just quicker and easier to type sand amp rather than transistor amp,just as it's easier to type valve rather than thermionic device.

[Ali Tait]

Chris,I could put you in touch with someone who lives in Wokingham who would do the job at a good price.He's a retired broadcast engineer and does the repairs and builds of WD stuff amongst other things.Very little he doesn't know about amps.A very nice bloke too.

[Krisbee]

Thanks, that's most helpful. You have a PM.

[Barry]

It's not gibberish IMO.Some think it's a derogatory term-I don't mean it that way,it's just quicker and easier to type sand amp rather than transistor amp,just as it's easier to type valve rather than thermionic device.

For all you lazy buggers out there, "tube" requires less key-strokes than "valve"! ;)

Regards

[Ali Tait]

Aye,but I aint American!!